The Advanced Biofidelic Lower Extremity Kids prosthesis (ABLE Kids) project will advance the state-of-the-art of pediatric prosthesis systems by advancing the demonstrably successful Phase I device and refining it into an ultracompact and lightweight form factor suitable for pediatric use. Through the support of the Shriner's Hospitals in Salt Lake City, UT and Shreveport, LA, numerous prosthetists, and with the consultation of cutting edge researchers at Clarkson University, a highly adaptive device will be produced and commercialized suitable for childhood amputees with both traumatic and congenitial deficiencies. Specifically, ABLE Kids will result in a modular, microprocessor controlled, mesofluidic ankle joint that dynamically makes ankle control adjustments needed to optimize the dynamic function and safety of a child's prosthesis. Additionally, advanced algorithms will be developed to optimize the performance of non microprocessor controlled knees by adjusting ground reaction forces to optimize trigger point and release for knees in transfemoral pediatric subjects.